The neuroendocrine regulation of homeostasis of body weight and energy expenditure is achieved by integrating peripheral hormonal signals such as leptin and insulin, and central signals generated from hypothalamic regions including the arcuate nucleus, mediobasal nucleus and paraventricular nucleus (Woods S. C., et al., 1998, “Signals that regulate food intake and energy homeostasis”, Science, 280:1378-1383; Flier J. S., et al., 1998, “Obesity and the hypothalamus: novel peptides for new pathways”, Cell, 92:437-440).
Within the neuroendocrine regulatory pathway, the melanocortin system of the arcuate nucleus is of major importance. Melanocortin receptors (MC-R) have been identified in these hypothalamic regions. Pro-opiomelanocortin (POMC) containing neurons project to the arcuate nucleus to provide multiple neuropeptide neurotransmitters to stimulate these receptors. MC-Rs belong to the G-protein coupled receptor (GPCR) superfamily that contains a seven transmembrane structure. One unique characteristic that differentiates MC-Rs from other GPCRs is that endogenous antagonists/inverse agonists for these receptors have been discovered.
Striking evidence of endogenous antagonists/inverse agonists for MC-Rs has emerged from studies of the agouti protein, which exerts its effects through interacting with MC-R with competitive antagonism of the natural ligand alpha-MSH (Bultman S J, et al. 1992 “Molecular characterization of the mouse agouti locus”, Cell, 71:1195-1204; Lu, D., et al., 1994, “Agouti protein is an antagonist of the melanocyte-stimulating-hormone receptor”, Nature, 371:799-802; Brash G., 1999 “From the agouti protein to POMC-100 years of fat blonde mice”, Nat. Med., 5:984-985). The discovery of Agouti-related peptide (AgRP), an agouti protein homologue, that interacts specifically with subtypes of MC-Rs (MC-3R and MC-4R) and antaqonizes MC-4R but not MC-1R further suggests that the central MC-R are involved in body weight regulation. (Ollmann, M. M., et al., 1997, “Antagonism of central melanocortin receptors in vitro and in vivo by agouti-related protein”, Science, 278:135-138).
Five subtypes of MC-R (MC-1R-MC-5R) have been identified. Multiple POMC peptides are agonists on these receptors with overlapping activity (Adan Rah, et al., 1994, “Differential effects of melanocortin peptides on neural melanocortin receptors”, Mol Pharmacol., 46:1182-1190). MC-1R is primarily located in the peripheral nervous system. ACTH is the endogenous agonist for MC-2R, but is without much activity on other MC-R subtypes (Schioth H B, et al., 1997, “The melanocortin 1, 3, 4 or 5 receptors do not have a binding epitope for ACTH beyond the sequence of α-MSH”, Endocrinology, 155:73-78). MC-3R and MC-4 and -5 are mainly located in the CNS, with high concentrations in the hypothalamic regions such as the arcuate nucleus and paraventricular nucleus (Mountjoy K. G., et al., 1994, “Localization of the melanocortin-4 receptor (MC-4R) in neuroendocrine and autonomic control circuits in the brain”, Mol Endocrinol., 8:1298-1308). Multiple lines of evidence indicate that hypothalamic MC-4R and MC-3R play a key role in regulating food intake and energy balance. Ectopically expressing Agouti peptide Avy mouse causes a lethal syndrome characterized by pronounced obesity and the development of diabetes and neoplasms (Lu, D., et al., 1994, “Agouti protein is an antagonist of the melanocyte stimulating-hormone receptor”, Nature, 371:799-802). Transgenic mice over-expressing AgRP are obese, suggesting that blocking MC-3R or MC-4R is the cause of obesity. Further determination that MC-4R knock out mice (Brash, G., 1999 “From the agouti protein to POMC-100 years of fat blonde mice”, Nat Med., 5:984-985; Huszar, D., et al., 1997 “Targeted disruption of the melanocortin-4 receptor results in obesity in mice”, Cell, 88:131-141) have a similar phenotype as that of AgRP over-expressing mice further confirms that MC-4R is a key component in the body weight regulation pathway whereas MC-3R seems to be more involved in energy regulation. Deficient synthesis of melanocortins causes obesity in human and mutant mice (Krude, H., et al., 1998, “Severe early-onset obesity, adrenal insufficiency and red hair pigmentation caused by POMC mutations in humans”, Nat Genet., 19:155-157; Yaswen L, et al., 1999, “Obesity in the mouse model of pro-opiomelanocortin deficiency responds to peripheral mela-nocortin”, Nat. Med., 5:1066-1070). Moreover, in animal models of obesity treatment with αMSH like agonist induced weight loss (Benoit S. C., et al., 2000, “A novel selective melanocortin-4 receptor agonist reduces food intake in rats and mice without producing aversive consequences”, J. Neurosci., 20:3442-3448).
In humans, mutations of the MC-4R have been identified in obese patients and linked to impaired ligand binding and signaling (Hinney, A., et al., 1999, “Several mutations in the melanocortin-4 receptor gene including a nonsense and a frameshift mutation associated with dominantly inherited obesity in humans”, J. Clin. Endocrinol. Metab., 84:1483-1486; Gu, W., et al., 1999, “Identification and functional analysis of novel human melanocortin-4 receptor variants”, Diabetes, 48:635-639; Krude, H., et al., 1998, “Severe early-onset obesity, adrenal insufficiency and red hair pigmentation caused by POMC mutations in humans”, Nat Genet., 19:155-157).
Aberrant regulation of body weight, such as that in obese patients, is associated with physiological and psychological disorders. Therefore, it is desirable to find drugs that can regulate central melanocortin system and therefore treat related medical disorders. Here, we report the finding of compounds that can modulate MC-R/AgRP/αMSH system.